Diesel aftertreatment devices such as catalyzed diesel particulate filters (CDPF) and NOx adsorber catalysts (NAC) are known in the art for controlling diesel engine emissions. During diesel engine operation, oxides of nitrogen and carbon particulates are produced as byproducts of combustion. These materials are subsequently collected by the NAC and the CDPF. As the oxides of nitrogen and carbon particulates accumulate within these aftertreatment devices, the aftertreatment devices must be regenerated. This is accomplished by reducing the oxides of nitrogen and oxidizing the carbon particulates held by these devices.
NAC devices are commonly regenerated by running the diesel engine rich, a few seconds for every minute of engine operation, to provide reducing agents capable of reducing the oxides of nitrogen stored in the NAC. However, as the engine runs rich, fuel may be wasted and the additional fuel may be completely oxidized or generate excess smoke before the reducing agents are used to regenerate the NAC.
CDPF devices require regeneration at much longer intervals, such as every 200 miles of vehicle operation. Regeneration of a CDPF is usually accomplished by injecting fuel into engine cylinders during their exhaust cycle to form fuel vapors which are carried with exhaust gas for burning in the CDPF. However, depending upon timing and engine operating conditions, the after injected fuel may be completely oxidized or generate smoke before the fuel vapor reaches the CDPF.
A proposed method of regenerating a CDPF is after-injection, which involves injecting low pressure diesel fuel directly into the exhaust downstream of the engine. However, depending on exhaust gas temperatures, injected fuel may not fully vaporize, resulting in the formation of carbon buildup in the exhaust system.